Tyrande Whisperwind is the high priestess to Elune and thus after the fall of Queen Azshara, is now the leader of the Night Elves (or Kaldorei in their native tongue).
Tyrande grew up with both Malfurion and Illidan in the city of Suramar and the three fought against the Burning Legion in the War of the Ancients.
After Illidan created a second Well of Eternity, he was imprisoned for 10,000 years. However, because of the second invasion of the Burning Legion, Tyrande released him in hopes he could help stop them. He agreed to help as his love for her never stopped. Malfurion was against the idea fearing his brother was still corrupt but Illidan tried to prove himself.
Once Illidan fought Arthas in Felwood, Arthas mentioned the Skull of Gul'dan which corrupted the entire forest. Illidan headed for the Skull of Gul'dan but instead of destroying it after killing several demons, he absorbed its powers believing his now increased powers would redeem himself in Tyrande's eyes. After absorbing its powers, he killed Tichondrius, ending the demonic invasion in Felwood. Despite ending the invasion, Malfurion and Tyrande were horrified at what Illidan had become and Malfurion baninshed Illidan from Felwood, with no objections from Tyrande. Before he left, Illidan told Tyrande no matter what form he takes, he would always look out for her.
Despite his lust for power and being labled a villain, Illidan's love for Tyrande made him go against the Legion twice and turn against Queen Azshara herself, and thus his love for her made him one of the least evil villains in the Warcraft franchise.